The initialization and event handler

CmsNotificationManager.cs

public class CmsNotificationManager
{
	private static Dictionary<string, string> EventMessages;

	public static void Initialize()
	{
		EventMessages = new Dictionary<string, string>();

		Database database = Factory.GetDatabase("master");

		foreach (ID selectId in database.DataManager.DataSource.SelectIDs(null, WebhookIDs.WebhookHandlerTemplate))
		{
			Item obj;

			using (new SecurityDisabler())
			{
				obj = database.GetItem(selectId);
			}

			if (!obj.Name.Equals("__Standard Values", StringComparison.OrdinalIgnoreCase) && new CheckboxField(obj.Fields[WebhookFieldIDs.Enabled]).Checked && new CheckboxField(obj.Fields["Is Notification Enable"]).Checked)
			{
				SubscribeEvents(GetIdsFromString(obj.Fields[WebhookFieldIDs.Events].Value), obj);
			}
		}
	}

	private static ICollection<string> GetIdsFromString(string value) => value.Split(new char[1]
	{
	  '|'
	}, StringSplitOptions.RemoveEmptyEntries);

	private static void SubscribeEvents(ICollection<string> ids, Item item)
	{
		var action = new Action<string, EventHandler>(Event.Subscribe);

		foreach (string id in ids)
		{
			Database database = item.Database;
			
			Item obj;
			
			using (new SecurityDisabler())
			{
				obj = database.GetItem(id);
			}

			if (obj == null)
			{
				return;
			}
			else
			{
				var eventName = obj[WebhookFieldIDs.EventName];

				var eventMessage = obj["Event Message"];

				if (!string.IsNullOrEmpty(eventName))
				{
					action(eventName, new EventHandler(CmsNotifier));

					if (string.IsNullOrEmpty(eventMessage))
					{
						eventMessage = "[Default] :: Event has been processed";
					}

					EventMessages.Add(eventName, eventMessage);
				}
			}
		}
	}

	private static void CmsNotifier(object sender, EventArgs args)
	{
		var shellSite = SiteContext.GetSite("shell");

		using(new SiteContextSwitcher(shellSite))
		{
			var parameters = args as SitecoreEventArgs;

			var message = EventMessages[parameters.EventName];

			var script = $"toastr.info('{message}')";

			var page = Context.Page;

			try
			{
				if (Context.ClientPage != null)
				{
					var clientPageTypeName = Context.ClientPage.GetType().Name;

					if (clientPageTypeName.Equals("sitecore_shell_applications_content_manager_default_aspx") || Context.ClientPage.ClientQueryString.Contains("Installer.InstallPackage"))
					{
						Context.ClientPage.ClientResponse.Eval(script);
					}
				}                    
			}
			catch(Exception ex)
			{
				Log.Error($"[CMSNOTIFICATION] :: An error occurred in {nameof(CmsNotificationManager)}.\n\rMessage: {ex.Message}.\n\rStackTrace: {ex.StackTrace}.\n\rInnerException: {ex.InnerException}", nameof(CmsNotificationManager));
			}                
		}            
	}
}